Sound reproducing instrument



- Feb. 8, 1 944.

G. HOLLAND SOUND REPRODUCING INSTRUMENT Filed NOV. 16, 1940 i INVENTOR ATTORNEY Patented Feb. 8, 1944 2,341,275 SOUND arrnonucmc nvs'l:m'nmzu'r Glen Holland, Bronxville, N. Y. Application November 16, 1940, Serial No. 365,929

12 Claims.

This invention relates to a sound reproducing instrument of the type utilizing a voice coil which is adapted to vibrate relatively to a magnetic field when' electric current of audio frequency is conducted through the voice coil.

(Cl. 17a 115. s)

More particularly, my invention relates to means whereby vibrations in a voice coil may be imparted to any suitable sound producing medium, as, for instance, a table top, a pane of plate glass, or any other body which will act as a soundingboard. Even more particularly, my invention contributes to the art a voice coil assembly which may be readily applied to any suitable medium for transmitting sound through said medium.

As a feature of 'my invention, I secure to a voice coil a stylus, which may have any particular shape desired, depending on the medium to which the vibrations of the coil are to be transmitted, and through this stylus, I transfer the vibrations of the voice coil to the particular desired medium. While I have foundit possible, with actual structures which I have built incorporating my invention, to transfer the voice coil vibrations to many mediums, I have concentrated especially on the transmission of the vibrations to plate glass windows. This manner of utilizing my invention has great commercialvalue, since.

sound may readily be transmitted by the voice coil within a store window to the plate glass window, and therefore to the outside of a store. An application of this class is particularly desirable for advertising, for the giving of demonstrations, and for other uses which will occur to those skilled in the art.

As a feature of my invention, the voice coil of my instrument is yleldingly supported rela-.

tively to what I prefer to call a base member,

and with a portion of the voice coil within a magnetic field maintained by means supported on the base member. The stylus which is mounted on the voice coil, may be applied to aplate glass window, for example, and with the'yieldlng /the vibrations of the voice coil. It may be well to point out that the initial stress of the yielding supporting means of the voice coil, maintains the stylus firmly pressed against the plate glass window so that there will be no relative motion between the stylus and the window,'which motion would create a knocking and pounding effect and would prevent an effective transmission of the-sound vibrations, all as will be well. appreciated by those'skilled in the art.

As a feature of my invention, I utilize a rather novel means for mounting the voice coil relatively to the base member. In one modification,

I utilize wires maintained under tension for holding the voice coil in a central initial position in the magnetic field relatively to which it vibrates. In a second modification, I secure the voice coil relatively to a core member mounted in the magnetic field through what I prefer to call a rubber bearing. This rubber bearing may be fabricated from highly resilient sponge rubber, or conceivably from some suitable artificial product having properties similar to sponge rubber.

As a further feature of my invention, I provide means for protecting the magnetic field from the entrance of foreign particles therein, all as will be set forth hereinafter- I have thus set forth the general theory of operation of my invention, and its particularly outstanding features in order that the specific forms of mechanisms embodying my contribution to the art which I shall. hereinafter describe, may be better understood.

For a description of specific preferred forms form of my invention. Fig. 5 is a sectional view taken along lines 5-5 of Fig. 4.

' supporting means under stress through the suit- Referring now more particularly to the drawing, and especially Figs. 1, -2 and 3, the base member of my invention is designated generally by reference numeral 10, and is preferably formed 1 of a single casting having a circular base plate v H and four radially and outwardly extending arms "terminating in a circular peripheral portion l3. ,For maintaining the magnetic field already discussed generally, I use a circular magnet It, which may be formed of some suitable highly magnetic material, such as Alnico or Nipermag. The magnet I4 is suitably housed between circular low carbon steel plates l5 and plates to the base plate I l' of the base member III, as by a series of bolts which are not illustrated in the modification of Fig. 3, but which are shown in the modification of Figs. 4 and 5, and to which reference will be made later.

A central low carbon steel plug H is secured as by a pressed fit at i8 relatively to the plate,

I5, and is spaced relatively to a central circular opening is in the plate 96 to allow vibrating movement of a' sleeve portion 29 oi the voice coil assembly V relativelyto the magnetic field maintained by magnet M. Actually, the space between the plug i7 and the peripheral surface of the opening IBoi'the plate I6 may be as little as .020". v

The sleeve 28 of the voice collrassembly V is preferably formed of aluminum, as is an extending cone portion 2! thereof. Secured to the cone portionZl is what I term a stylus 22, which is merely threaded into the end of the cone and then locked by a nut 23. Sufiice it to say that the stylus 22 vibrates with the cone 2! and the sleeve portion 2G as audio frequency current traverses the wire coil 24 wound about the sleeve portion of the voice coil assembly,

' all in a manner which will be well understood by those skilled in the art. For supplying current to the voice coil, there is utilized a suitable plug member 25 from which wires 26 and 27 extend to the wire coil 24.

The voice coil assembly is held yieldingly by wires 28 and 29 in a predetermined position relatively to the magnetic field maintained by the magnet i i. Each of these wires fits within a portion of a groove 30 on the cone 2!! of the voice coil assembly V, the ends of the wires extending through holes 3i formed in the arms l 2, and into winding relation to screws 32 threaded at 34 into the arms i2. Lock nuts 35 secure the screws in any rotated adjusted position. It is obvious that by rotating the screws 32, the tension in the wires 28 and 2s may be increased or decreased to properlycenter the voice coil, and to determine the degree of tension with which it will be maintained in its predetermined normal axial position relatively to the magnetic field and the core ii, which predetermined normal position is shown in dotted lines in Fig. 3. It will be noted that the voiceco'il assembly V in its dotted line position of' Fig. 3, the stylus 22 will lie beyond the plane of the medium to which the vibrations of the coil are to' be transmitted when the peripheral portion B of the base member ii) is applied against the said medium. The application of the base member thus places the wires 28 and 29 under tension, and moves the voice coil out of its predetermined normal position. Incidentally, 'in Figs. 2 and 3, the medium is designated by the reference letter G, and is intended torepresent a plate glass window.

In applying my sound reproducer to the plate glass window G, I place the base member I against the window until a circular washer 36 fitting against the circular peripheral portion it of the said base member, lies firmly against the glass G. In this position, the voice coil and the stylus 22 willmove to the right relatively to the base member, as is best illustrated in Figs. 2 and 3, the wires 28 and being stressed or tensioned as the voicecoil and stylus so move relatively to the base member lfl. It will be readily appreciated that if the voice coil now vibrates relatively to the base member l0 and the magnetic held, and since all vibrations will will naturally traverse the wire 24a be toward the plate glass, it will have no'motion relatively to that plate glass, thereby avoiding any hammering of the stylus against the plate glass. Actually, the vibrations of the voice coil will be accurately transmitted through the stylus to the plate glass window, the plate glass window acting as a sounding board, or diaphragm. Those on the outside of the window will hear reproduced the particular sounds intended to be reproduced by the voice coil. I

For holding the base I of the sound reproducer against the plate glass windom'l prefer to use a. series-oi four vacuum cups 3! each secured throug hthe medium of a bracket 38 to the peripheral member l3 of the base [8 of my instrument. The structure or the vacuum cups is shown, but need not be described in detail, it being quite apparent to those skilled in the art that when the actuating arm 39 of each of the vacuum cups is rotated, its cam portion II will raise the central part of the rubber vacuum cup 3i to hold the base member 10 firmly against the plate glass window, and of course with the wires 28 and 29 stressed, as has already been described. Naturally, securing means other than vacuum cups may be used if desired, and it is conceivable that in some installations where the instrument is to be used Ijace downward, the mere weight of the instrument will be sutlicient to apply the initial stress required.

In the modification oi. Figs. 4 and 5, I use a base member in the form of a plate 45, at the ends of which are maintained the vacuum cups 3i. Secured to this base member throughthe intermediary of the bolts 42 is a plate 48, the said bolts passing through an annular flange M extending from a separator plate 45. A magnet 46, similar to the magnet id of my first modification, is secured to the plate 43 and therefore to the base member 45, by a series of four bolts "all extending into a back retaining plate :38. El central plug Illa, similar to the plug it of the first modification, is secured to the plate i-8, just as the plug ill in the first modification is secured to the plate F15.

The voice coil assembly V2 of my modification of Figs. 4 and 5 is quite similar to that of Fig. 3,

and is clearly shown in Fig. 5 as having a cone portion 25a and a sleeve the on which is woundany equivalent artificial material, so that it may yield to allow movement of the voice coil assembly and the stylus 22a thereof out of a normal position when the sound reproducer is applied to a plate glass window G, as in Fig. 5, for transmitting sound through the medium of said glass. The application of the instrument to the glass, as by vacuum cups 31, places the rubber bearing 50 under compression sufficient to maintain the stylus 22a firmly against the plate glass window G, as shown in Fig. 5. Audio frequency current i of the voice coil assembly, effecting a vibration of the voice coil and. the stylus 22a the vibrations being transmitted to the plate glass window G as'in the case of the first modification.

In the modification of Fig. 5, the base plate II is formed with a small opening 52, through which plate 4| to prevent, so far as is possible, the entrance of particles into the field of the magnet 46. In the modification of Figs. 1, 2 and 3, the

same result is obtained by a suitable diaphragm 53, which may be formed of cloth or screening, or any other material adapted for the purpose, it being quite clear that the diaphragm 53 is secured as through cementing at 54 to the periphery of the cone 2i of the voice coil assembly V, and by cementing at 55 to the base plate I I, it being quite clear that in this position, it functions quite well for the purpose for which it is intended.

While I have shown and described twoparticular forms of my invention which I prefer to utilize, those skilled 'in the art will readily understand how my contribution to the art may readily be embodied in other structures. I therefore expect to obtain a monopoly which will prevent the utilization of my contribution in physical forms other than those herein illustrated.

I now claim:

1. In a combination of the class described, a moving coil, abase member, means on said base member maintaining a magnetic field, tension wires extending between said coil and base member for yieldingly supporting said coil on said base member for movement relatively to said magnetic field, a stylus, means securing said stylus to said coil for movement therewith and through which the vibrations of said coil may be transferred to a suitable medium, and means for securing said base member to said medium with said stylus maintained pressed against said medium through the initial tensioning of said wires.

2. In a combination of the class described, a moving coil, a base member, means on,said base member maintaining a magnetic field, tension wires extending between said coil and base member for yieldingly supporting said coil on said base member in a predetermined normal position relatively to said magnetic field and for movement relatively to said magnetic field, a stylus, means securing said stylus to said coil for movementv therewith and through which the vibrations of said coil may be transferred to a suitable medium, and means for securing said base member to said medium with said stylus maintained pressed against said medium and out of its said predetermined normal position through the initial tensioning of said wires.

3. A device adapted for application to a sound producing medium comprising a moving coil, a base member, means on said base member maintaining a magnetic field, a readily compressible and expansible rubber bearing interposed between said coil and said base member for yieldingly supporting said coil on said base member for movement through said bearing relatively to said magnetic field, a stylus secured to said coil for moveposition relatively to said magnetic field and for movement through said bearing relatively to said magnetic field, a stylus secured to said coil for movement therewith and through which the vibrations of said coil are transferred to said medium, said stylus projectingbeyond the contact surface of said base member when said coil is in its normal position, and means for -securing said base member with its contact surface against said medium and said stylus pressed by said medium out of its said predetermined normal positionthrough the initial compression of said rubber bearing.

- 5. A device adapted for application to a sound producing medium comprising a moving coil, a base member, means on said base member maintaining a magnetic field, a metal core for said field secured to said base, a readily compressible and expansible rubber bearing interposed between said coil and said metal core for yieldingly supporting said coil on said metal core in a predetermined normal position relatively to said magnetic field and for movement through said bearing relatively to said magnetic field, a stylus secured to said coil for movement therewith and through which the vibrations of said coil may be transferred to said medium, and means for securing said base member to said medium with said stylus maintained pressed against said medium and out of its said predetermined normal position through the initial compression of said rubber bearing.

,bration' in said magnetic field, a stylus on the ment therewith and through which the vibrations base member having a contact surface adapted to lie against said sound producing medium, means on said base member maintaining a magnetic field, a readily compressible and expansible rubber bearing interposed between said coil and said base member for yieldingly supporting said coil on said base member in a predetermined normal 76 6. A device adapted for application to a sound producing medium comprising a moving coil, a

base member, means on said base member maintaining a magnetic field, means yieldingly supporting said coil on said base member for movement relatively to said magnetic field, a diaphragm-like barrier extending from the periphery of said coil to said base member for protecting said magnetic field against the entrance of metal particles therein, a stylus secured to said coil for movement therewith and through which the vibrations of said coil may be transferred to a suitable medium, and means for securing said base member to said medium with said stylus maintained pressed against saidmedium through the initial stressing of said means yieldingly supporting said coil.

7. A device adapted for application to a sound producing medium to impart sound vibrations thereto, comprising a base member having a medium contacting surface, means on said base member maintaining a magnetic field, a moving coil, yielding means supporting said coil for viend of said coil, saidyielding means holding said coil in a normal position in which its stylus extends beyond the medium contacting surface of said basemember so as to be first to contact the medium as the base member is applied toward said medium whereby to prevent the securing of said base member to said medium until said stylus and coil are pressed back from said normal position through the stressing of said yielding means supporting the coil on tlie base member, and means for securing said base member with its medium contacting surface against said medium and with said stylus and coil pressed by the medium out of said normal position relatively to said-,base member through the stressing of said yielding means.

- 8. A device adapted for application to a sound producing medium to impart sound vibrations thereto, comprising a base member,;medium engaging means secured on said base member,

means on said base member maintaining a magnetic field, a moving coil, supporting means yieldingly supporting said coil i'or vibration in said magnetic fieid, a stylus on the end of said coil, said supporting means holding said coil in a normal position in which its stylus extends beyond said medium engaging means of said base member so as to be the first to contact the medium as the-base member is applied toward said medium, said stylus and coil moving back from said normal position through the stressing of said supporting means by-said medium as said medium engaging means effect engagement of said medium to support said base member on said medium while said stylus vibrates the medium.

9. A device adapted for application to a sound producing medium to impart sound vibrations thereto, comprising a base member, a series of securing devices spaced peripherally about said base member, means on said base memmr maintaining a magnetic held, a moving coil, supporting means yieldingly supporting said coil for vibration in said magnetic field, a stylus on the end of said. coil, saicisupporting means holding said coil in a normal position so as to be the first to contact the medium as the base member is applied toward said medium, said stylusv and coil moving back from said normal position through the stressing of said supporting means by said medium as said series of securing devices secure the said base member on said medium.

10. A device adapted for application to a sound producing medium to impart sound vibrations thereto, comprising a base member, a series of vacuum cups spaced peripherally about said base 3 member, means on said base member maintain- 5 magnetic field. 7

ing a magnetic field, a moving coil. supporting,

means yieldingly supporting said coil for vibratlon in said magnetic field, a'stylus on the end.

01' said coil, said supporting means holding said 5 coil in a normal position in which its stylus extends beyond said vacuum cups of said base memher so as to be the first to contact the medium as the base member is applied toward said medium. said stylus and coil moving back from said 10 normal position through the stressing of said supporting means by said meduirn as said vacuum cups are stressed to secure said base member to said medium.

11. .In a device of the class described, a. base member, means on said base member maintaining a magnetic field, a coil adapted to move in said magnetic field, a cylindrical support piece on said coil, and wires extending from said base member and into contact with. opposed portions'of the 2g circumference of said cylindrical support piece for holding said moving coil in said magnetic field and for movement therein through the stressing of said wires.

12. In a device of the class described, a base member, means on said base member .inaintaininga magnetic field, a coil adapted to move in said magnetic field, a cylindrical support piece on said coil, and wires for securing said moving coil in 'said magnetic field and for movement therein, each wire being fixed at its opposite ends I to spaced parts or said base member and extending about a portion of the periphery of said support piece, the cumulative effect of said wires being to centralize and hold said moving coil in said GLEN 'HOLLAND. 

